Probing the Charge Carrier Dynamics in Ni@NiS/p-Type C₃N₄ Heterostructure: Implications for Enhanced Photocatalytic Hydrogen Evolution

Carbon nitride (C3N4) has been regarded as one of the most extensively studied materials for photocatalytic hydrogen production. However, the inherent poor crystallinity of pure C3N4 hinders charge transfer and promotes the rapid recombination of photogenerated carriers. Additionally, the migration of photogenerated holes to the surface of n-type C3N4 is detrimental to photocatalytic hydrogen evolution. In this study, we successfully synthesized the p-type C3N4 (Li–K) via a molten-salt method to adjust the energy band structure that allows photogenerated electrons to migrate toward the surface of C3N4 (Li–K). Subsequently, a Ni@NiS core–shell cocatalyst was loaded to capture these electrons. The optimized NiS-5 photocatalyst exhibits an excellent photocatalytic hydrogen evolution rate of 18.18 mmol h–1 g–1 under visible light, approximately 33-fold and 2.5-fold higher than those of C3N4 (Li–K) and NiS-0, respectively. This exceptional performance stems from the efficient transfer of separated photogenerated charges: the well-matched energy bands between C3N4 (Li–K) and NiS enable smooth charge migration from C3N4 (Li–K) to Ni and then to NiS, significantly enhancing the separation efficiency of photogenerated carriers. This work provides a promising strategy for synthesizing highly efficient p-type carbon nitride-based photocatalysts.